Flow of a rarefied gas past a circular cylinder

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Abstract
The flow of a rarefied gas past a circular cylinder at low Mach numbers is studied on the basis of the linearized Bhatnager–Gross–Krook model equation. The flow field is divided into two regions: the kinetic region adjacent to the cylinder and the near continuum region outside it. The Oseen–Stokes equation is treated in the near continuum region. In the kinetic region, the simultaneous integral equations for the flow velocity, density, and temperature are derived from the model equation. These equations are solved numerically by matching with the Oseen–Stokes solution. The distributions of the flow velocity are obtained for a wide range of the Knudsen numbers. The drag on the cylinder is also calculated and is favorably compared with the previous formulas valid for small and large Knudsen numbers.